CHAPTER XXII.

METEOROLOGY.

India.

THE great peninsula of India, with its lofty mountain ranges Meteorand its extensive seaboard, exposed to the first violence of ology of the winds of two oceans, forms an exceptionally valuable and interesting field for the study of meteorological phenomena. But the Department of Government which deals with these phenomena has had to contend with many obstacles; and it is only within the last few years that trustworthy statistics have been obtained for a complete system of registration stations. Every year, however, is now adding to our knowledge of the meteorology of the country, and supplying fresh authentic materials for purposes of comparison and induction.

Meteorological Geography.-After the general description of the country given at the beginning of this volume, it is only gical Geonecessary to sketch very briefly the meteorological geography graphy. of India. The following paragraphs are condensed from an interesting account in the official Report on the Meteorology of India (for 1875), by Mr. H. F. Blanford. The great mountain ranges of the HIMALAYAS and the SULAIMANS, which form the northern and north-western boundaries of India, have been fully described.1 From the gorge of the Indus to that of the Dihong (Brahmaputra), a distance of 1400 miles, the Himalayas form an unbroken watershed, the northern flank Himáof which is drained by the upper valleys of these two rivers; layas. while the Sutlej (Satlaj), starting from the southern foot of the Kailás peak, breaks through the watershed, dividing it into

1 See ante, pp. 26-30; also articles HIMALAYAS and SULAIMAN, Imperial Gazetteer, vols. iv. and viii.

Himá

two very unequal portions, that to the north-west being the smaller. The average elevation of the higher Himalayas may be taken at not less than 19,000 feet, and therefore equal to the height of the lower half of the atmosphere; indeed, few of the passes are under 16,000 or 17,000 feet. Across this mountain barrier there appears to be a constant flow of air, more active in the day-time than at night, northwards to the arid plateau of Tibet. There is no reason to believe that any layan air transfer of air takes place across the Himalayas in a southerly direction; unless, indeed, in those elevated regions of the atmosphere which lie beyond the sphere of observation. But a nocturnal flow of cooled air, from the southern slopes, is felt as a strong wind where the rivers debouch on the plains, more especially in the early morning hours. This current probably contributes to lower the mean temperature of the belt of the plains which fringes the mountain zone.

currents.

Eastern Himálayas.

Western Himálayas.

Vapour

bearing winds.

The Eastern Himálayas present many points of contrast with the western parts of the range. The slopes of the Sikkim and Bhután Hills, where not denuded for the purposes of cultivation, are clothed with a dense impenetrable forest, which at the lower levels abounds in figs, rattans, and representatives of a tropical humid climate. At higher levels they are covered with oaks, chestnuts, magnolias, pines, etc., of the most luxuriant growth.

In the Western Himalayas, on the other hand, the spurs of the outer ranges are more sparsely clad with forest, especially on their western faces; and naked precipitous crags are of constant occurrence. The vegetation of the lower and warmer valleys, and of the fringing belt (the Tarái), is comparatively thin, and such as characterizes a warm but dry region. Pines of several species form a conspicuous feature of the landscape at lower levels. It is chiefly the outer ranges that exhibit these contrasted features; and they depend partly on the difference of latitude, but mainly on that of the rainfall. In Sikkim and Bhután this is abnormally copious, and is discharged full on the face of the range. As the chain recedes to the north-west, the greater is the distance to be traversed by the vapour-bearing winds in reaching it, and the more easterly is their direction. For such winds, whether coming from the Bay of Bengal (apparently their principal source) or from the Arabian Sea, turn on reaching the Gangetic valley, and blow more or less parallel to its axis and that of the mountain range.

The country on either side of the Suláimán range is

frontier.

characteristically arid. Dry winds from the desert tracts of Punjab Persia and Buluchistán predominate throughout the year. The scanty cultivation on the hills is dependent on the winter snows, or the rare showers which reach them from the eastward, or on the supply of the larger local streams. The lower plains would be uninhabitable but for the fertilizing irrigation furnished by the great river that traverses them.

desert.

At the foot of the great Himalayan barrier, and separating it from the more ancient land which now forms the highlands of the peninsula, a broad plain, for the most part alluvial, stretches Indus from sea to sea. On the west, in the dry region, this is plain. occupied partly by the alluvial deposits of the Indus and its tributaries; by the saline swamps of Kachchh (Cutch), by the rolling sands and rocky surface of the desert of Jaisalmír The great (Jeysulmere) and Bikáner, and partly by the more fertile Indian tracts to the eastward. Over the greater part of this region rain is of rare occurrence; and not infrequently more than a year passes by without a drop falling on the parched surface. On its eastern margin, however, in the neighbourhood of the Aravalli Hills, and again on the Northern Punjab, rain is more frequent, occurring both in the south-west monsoon, and also at the opposite season in the cold weather. As far south as Sirsa and Múltán, the average rainfall does not much exceed 7 inches.

The alluvial plain of the Punjab passes into that of the Gangetic Gangetic valley without visible interruption. Up or down this plain. plain, at opposite seasons, sweep the monsoon winds, in a direction at right angles to that of their nominal course; and in this way the vapour brought by winds from the Bay of Bengal, is discharged as snow and rain on the peaks and hill-sides of the Western Himálayas. Nearly the whole surface is under cultivation; and it ranks among the most productive as well as the most densely populated regions of the world. The rainfall diminishes from 100 inches at the south-east corner of the Gangetic delta to less than 30 inches at Agra and Delhi, and there is an average difference of from 15 to 25 inches between the northern and southern borders of the plain.

Eastward from the Bengal delta, two alluvial plains stretch Eastern up between the hills that connect the Himalayan system with Bengal. that of the Burmese peninsula. The first is that of Assam and the Brahmaputra, long and narrow, bordered on the north by the Himalayas, on the south by the lower plateau of the Gáro, Khásí, and Nágá Hills. The second, or Sylhet and Cáchár

valley, is chiefly occupied by swamps and jhils, and separates the Gáro, Khásí, and Nágá Hills from those of Tipperah and the Lushái country. The climate of both these plains is damp and equable, and the rainfall is prolonged and generally heavy, especially on the southern slopes of the hills. A meteorological peculiarity of some interest has been noticed, more especially at the stations of Sibságar and Silchár, viz. the great range of the diurnal variation of barometric pressure, particularly during the cool months of the year. It is the more striking, since at Rúrki, Lahore, and other stations near the foot of the Himálayas, this range is less than on the open plains. Central The highlands of the peninsula are cut off from the table-land. Himalayan ranges by the Indo-Gangetic plain. They are divided into two unequal parts, by an almost continuous chain of hills, loosely known as the Satpura range, running across the country from west-by-south to east-by-north, just south of the Tropic of Cancer. This chain may be regarded as a single feature, forming the principal watershed of the peninsula. The waters to the north of it drain chiefly into the Narbada (Nerbudda) and the Ganges; those to the south, into the Tápti, the Godavari, the Mahanadi, and smaller streams. In a meteorological point of view, this central chain of hills is of much importance. Acting together with the two parallel valleys of the Narbada (Nerbudda) and Tápti (Taptee), which drain the flanks of its western half, it gives a more decided easterly and westerly direction to the winds of this part of India, and condenses a tolerably copious rainfall during the south-west

Satpura range.

Málwá

plateau.

Aravalli range.

monsoon.

Separated from this chain by the valley of the Narbada on the west, and that of the Son on the east, the plateau of Málwá and Baghelkhand occupies the space intervening between these valleys and the Gangetic plain. On the western edge of the plateau are the ARAVALLI Hills, which run from near Ahmedábád up to the neighbourhood of Delhi, and include one hill, Mount Abu, over 5000 feet in height. This range exerts an important influence on the direction of the wind, and also on the rainfall. At Ajmere, an old-established meteorological station at the eastern foot of the range, the wind is predominantly south-west. Both here and at Mount Abu the south-west monsoon rains are a regular phenomenon ; which can hardly be said of the region of scanty and uncertain rainfall which extends from the western foot of the range and merges in the Bikáner desert.

The peninsula south of the Sátpura range consists chiefly Southern

of the triangular plateau of the Deccan, terminating abruptly plateau. on the west in the Sahyadri range (Western Gháts), and shelving to the east (Eastern Gháts). This plateau is swept by the south-west monsoon after it has surmounted the western barrier of the Ghats. The rainfall is consequently light at Poona and places similarly situated under the lee of the range, and but moderate over the more easterly parts of the plateau. The rains, however, are prolonged to the north of the Satpuras three or four weeks later than in Southern India, since they are brought there by the easterly winds which blow from the Bay of Bengal in October and the early part of November; when the re-curved southerly wind ceases to blow up the Gangetic valley, and sets towards the Karnatic. This was formerly thought to be the north-east monsoon, and is still so spoken of by some writers; but the rainy wind is really a diversion of the south-west monsoon.

At the junction of the Eastern and Western Ghats rises the Anamalai bold triangular plateau of the Nilgiris, and to the south of Hills. them come the Anamalais, Palnis (Pulneys), and Travancore Hills. These ranges are separated from the Nilgiris by a broad depression or pass known as the Pálghát gap, some 25 miles wide; the highest point of which is about 1500 feet above the sea. This gap affords a passage to the winds, which elsewhere are barred by the hills of the Ghát chain. The country to the east of the gap receives the rainfall of the south-west monsoon; and during the north-east monsoon, ships passing Beypur meet with a stronger wind from the land than is felt elsewhere on the Malabar coast. According to Captain Newbold, this gap affords an outlet to those furious storms from the eastward which sweep the Bay of Bengal, and, after traversing the peninsula, burst forth through

it to the neighbouring sea.'

coast

In the coast-strip of low country which fringes the peninsula Southern below the Ghats, the rainfall is heavy, the climate warm and strips. damp, the vegetation dense and tropical. The steep slopes of the Ghats, where they have not been artificially cleared, are also thickly clothed with forest.

Ceylon should, for meteorological purposes, be included Meteorin our survey. The country both south and west of the ology of Ceylon. hills which occupy the south centre of the island is very

rugged down to the coast. The rainfall is here frequent and Rainy heavy; and the temperature being high and equable, the south-west vegetation is dense and very luxuriant, such as is characteristic

region.